Acrylonitrile polymer compositions stabilized with paraformaldehyde and trialkyl subsituted phosphites, and method of making same



ACRYLONITRILE POLYMER COMPOSITIONS STA- BILIZED WITH PARAFORMALDEHYDEAND TRIALKYL SUBSTITUTED PHOSPHITES, AND METHOD OF MAKING SAME PompelioA. Ucci and William H. Howard, Decatur, Ala.,

assignors to The Chemstrand Corporation, Decatur, Ala., a corporation ofDelaware No Drawing. Application December 17, 1956 Serial No. 628,489

17 Claims. (Cl. 260---32.6)

This invention relates to the stabilization of acrylonitrile polymersand blends thereof. More particularly,

it relates to the stabilization of acrylonitrile polymers and blendsthereof which have a tendency to develop "color upon standing orapplication of heat.

The term polymer, as employed in the instant demon solvents. In thoseinstances where suitable solvents have been found, in order to effectsolution, the application of heat is usually necessary. Where heat is'employed to effect solutions, from which shaped articles H are to beformed, a tan to dark brown color frequently develops in the solutionsand therefore is carried over into the product formed therefrom. Thiscolor also develops in solutions upon standing for prolonged periods oftime.

The mechanism which causes color formation has not been definitelyascertained, although a variety of reasons therefor have been advanced.The presence of "metal ions, copper and manganese in the solutions maycause the color. The employment of amide compounds as solvents mayresult in formation of amines when heat *is applied and cause color inthe compositions. purities present in the solvents have also been citedas a cause. Whatever may be the reason for color formation, it resultsin compositions and products of undesirable standards and therefore,hasbeen the source of concern, particularly in commercial operations wheresuch types of polymers or copolymers are employed.

Accordingly, it is an object of the present invention to preventundesirable color formation in acrylonitrile polymer compositions.

Uniteci States Patent ,ized with the inhibiting agents defined herein.

Another object is to minimize color formation when solutions of theacrylonitrile polymers are permitted to stand for a prolonged period oftime or upon the application of heat.

It is also an object of the invention to prevent color formation inacrylonitrile polymers at elevated temperatures.

' A still further object of the invention is the production :ofsolutions of acrylonitrile polymers and articles pro- -duced therefromhaving improved color characteristics. a

. Other objects and advantages will be apparent from a :consideration ofthe description of the invention which follows hereafter.

In general, the objects of the invention are accomplished by dissolvingthepolymer of acrylonitrile in a suitable solvent therefor andpreventing or minimizing color formation by the presence in the solutionas an inhibiting agent, a combined reagent comprising paraformaldehydeand an organic phosphite selected from -the group consisting of.triethyl phosphite, tribu'tyl phos- 2 phite, tris(2-ethylhexyl)phosphite, trihexyl phosphite and triisoctyl phosphite.

The components of the inhibiting agent may be emf ployed in equal orunequal amounts, any one constituent being present in a range of from 99to 1 percent in a two component system. The total amount of inhibitingagent may be employed in a range of about 0.1 to 20 percent, based onthe total polymer weight. However, it is preferred that the inhibitingagent of the instant invention be present in a small amount compared tothe amount of polymer dissolved. Thus, although the amount is notcritical, it is preferred that the inhibiting agent be present in theamount of about 0.1 to 10 percent, based on the total weight of thepolymer. The inhibiting agent may be added to the solvent before orafter the polymer is dissolved therein. The inhibiting agent permitsexposure to high temperatures for prolonged standing periods without thedevelopment of the objectionable color which usually results in suchsolutions. The compositions of the instant invention may be prepared ina varying temperature range. For example, the compositions of theinstant invention may be prepared by mixing the polymer, a suitablesolvent and the inhibiting agent at any temperature'or heating themixture to a temperature up to the boiling point of the solvent.

Among the solvents which may be used in practising the instantinventionare N,N-dimethylfo.rmamide, N,N- dimethylacetamide, aqueouszinc chloride, sulfuric acid, aqueous nitric acid, aqueous sodiumthiocyanate, ethyl- .ene carbonate, sulfolane, nitromethane, and thelike.

1 The polymeric materials, which may be employed in the practice of thepresent invention, are polyacrylo- .nitrile, copolyniers, includingbinary and ternary poly- .mers containing at least percent by weight ofacrylonitrile in the polymer molecule, or a blend comprisingpolyacrylonitrile or copolymers comprising acrylonitrile with from 2 to50 percent of another polymeric material, the blend having an overallpolymerized acrylo- Hnitrile content of at least 80 percent by weight.While the preferred polymers employed in the instant invention are thosecontaining at least 80 percent of acrylonitrile, generally recognized asthe fiber-forming acrylonitrile polymers, it will be understood that theinvention is likewise applicable to polymers containing less than 80percent acrylonitrile and the same stability is real- The acrylonitrilepolymers containing less than 80 percent acrylonitrile are useful informing films, coating com- H positions, molding operations, lacquers,and the like, in all of which applications the alleviation ofundesirable color is extremely important. For example, the polymer maybe a copolymer of from C 80 to 98 percent acrylonitrile and from 2 to 20percent of another monomer containing the C=C linkage andcopolymerizable with acrylonitrile. Suitable monololefinic monomersinclude acrylic, alpha-chloracrylic and ,methacrylic acids; theacrylates, such as methylmethacrylate, ethylmethacrylate,butylmethacrylate, methoxymethyl methacrylate, beta-chloroethylmethacrylate, and the corresponding esters of acrylic andalpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinylbromide, vinylidene chloride, l-chloro-l-bromoethylene; meth--acrylonitrile; acrylamide and methacrylamide; alpha- ,chloroacrylamide,or monoalkyl substitution products thereof; methyl vinyl ketone; vinylcarboxylates, such as vinyl acetate, vinyl chloroacetate, vinylpropionate, ,and vinyl stearate; N-vinylimides, such asN-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters;itaconic acid and itaconic ester; N-vinylcarbazole; vinyl furane; alkylvinyl esters; vinyl sulfonic acid; ethylene alpha, beta-dicarboxylicacids or their 'anhydrides acrylonitrile, methacrylonitrile, andZ-Vinylpyridine.

emulsion stabilizers.

or derivatives, such as diethylcitraconate, diethylmesaconate, styrene,vinyl naphthalene; vinyl-substituted tertiary heterocyclic amines, suchas the vinylpyridines and alkyl-substituted vinylpyridines, for example,2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, and thelike; l-vinylimidazole and alkyl-substituted l-vinylimidazoles, such as2-, 4-, or S-methyl-l-vinylimidazole, and other C=C containingpolymerizable materials.

The polymer may be a ternary interpolymer, for example, productsobtained by the interpolymerization of acrylonitrile and two or more ofany of the monomers, other than acrylonitrile, enumerated above. Morespecifically, and preferably, the ternary polymer comprises The ternarypolymers preferably contain from 80 to 97 percent of acrylonitrile, from1 to percent of a vinylpyridine or a l-vinylimidazole, and from 1 to 18percent of another substance, such as methacrylonitrile or vinylchloride.

The polymer may also be a blend of polyacrylonitrile or of a binaryinterpolymer of from 80 to 99 percent acrylonitrile and from 1 to 20percent of at least one other C=C containing substance with from 2 to 50percent of the weight of the blend of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to 90 percent of at least one otherC=C containing polymerizable monomer. Preferably, when the polymericmaterial comprises a blend, it will be a blend of a copolymer of 90 to98 percent acrylonitrile and from 2 to 10 percent of anothermono-olefinic monomer, such as vinyl acetate, which is not receptive todyestuff, with a sufficient amount of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to 90 percent of avinyl-substituted tertiary heterocyclic amine, such as vinylpyridine orl-vinylimidazole, to give a dyeable blend having an overallvinylsubstituted tertiary heterocyclic amine" content of from 2 to 10percent, based on the weight of the blend.

The polymers, useful in the practice of the present invention, may beprepared by any conventional polymerization procedure, such as masspolymerization methods, solution polymerization methods, or aqueousemulsion procedures. However, the preferred practice utilizes suspensionpolymerization wherein the polymer is prepared in finely divided formfor immediate use in the fiber fabrication operations. The preferredsuspension polymerization may utilize batch procedures, wherein monomersare charged with an aqueous medium containing the necessary catalyst anddispersing agents. A more desirable method involves the semi-continuousprocedure in which the polymerization reactor containing the aqueousmedium is charged with the desired monomers and the continuouswithdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any watersoluble peroxycompound, for example, the potassium, am-

monium and other water-soluble salts of peroxy acids,

sodium peroxide, hydrogen peroxide, sodium perborate, the sodium saltsof other peroxy acids, and any other water-soluble compound containing aperoxy group tends to make the resultant polymer more uniform in itschemical and physical properties.

Although the uniform distribution of the reactants throughout thereaction mass can be achieved by vigorous agitation, it is generallydesirable to promote the uniform distribution of'reagents by using inertwetting agents, or Suitable reagents for this purpose are thewater-soluble salts of .fatty acids, such as sodium oleate andpotassium. stearate, mixtures of water-soluble fatty acid salts, such ascommon soaps prepared by the saponification of animal and vegetableoils, the amino soaps, such as salts of triethanolamine anddodecylmethylamine, salts of rosin acids and mixtures thereof, thewater-soluble salts of half esters of sulfuric acid and long chainaliphatic alcohols, sulfonated hydrocarbons, such as alkyl arylsulfonates, and any other of a wide variety of wetting agents, which arein general organic compounds containing both hydrophobic and hydrophilicradicals. The quantity of emulsifying agents will depend upon theparticular agents selected, the ratio of mon omers to be used, and theconditions of polymerization. In general, however, from 0.01 to 1.0percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass orglass-lined vessels which are provided with a means for agitating thecontents. Generally rotary stirring devices are the most effective meansof insuring the intimate contact of the reagents, but other methods maybe successfully employed, for example, by rocking or tumbling thereactors. The polymerization equipment generally used is conventional inthe art and the adaptation of a particular type of apparatus to thereaction contemplated is within the province of one skilled in the art.The articles manufactured therefrom may be produced by well-knownconventional methods, for example, the

wet-spinning, dry-spinning and melt-spinning methods for producingfibers.

The following examples are illustrative rather than limitative and allparts, proportions and percentages are by weight unless otherwisespecified.

EXAMPLE I 25 grams of a polymer blend of 88 percent of a copolymercontaining 94 percent of acrylonitrile and 6 percent of vinyl acetateand 12 percent of a copolymer of 50 percent of acrylonitrile and 50percent of Z-methyl-S- vinyl pyridine 'were' added to milliliters ofN,N-dimethylacetamide containing approximately 1.0 gram of titaniumdioxide. The mixture was stirred and heated for 240 minutes at 100 C. Itwas then quickly cooled to room temperature and the color measured. Thissample was used as a control. The purity is set forth below.Subsequently, like samples were prepared but with 2.5 grams of a colorinhibitor containing 0.5 gram of paraformaldehyde and 2.0 grams of oneof the following: triethyl phosphite, tributyl phosphite, tris(2-ethy1hexyl) phosphite, trihexyl phosphite and triisoctyl phosphite.The purity is set forth below.

EXAMPLE II '25 .grams' of a copolymer containing 94 percent ofacrylonitrile and 6 percent of vinyl acetate were added to 100milliliters of N,N-dimethylacetamide containing approximately 1.0 gramof titanium dioxide. The mixture was stirred and heated for 240 minutesat 100 C. Itwas then quickly cooled to room temperature and the colormeasured. This sample was used as a control. The purity is set forthbelow. Subsequently, like samples were prepared but with 2.5 grams of aninhibiting agent containing 0.5 gram of paraformaldehyde and 2.0 gramsof one of the following: triethyl phosphite, tributyl phosphite, tris(Z-ethylhexyl) phosphite, trihexyl phosphite and triisoctyl phosphite.Thepurity. is set. forth below.

mam

Inhibitor Purity EXAMPLE m 20 grams of an acrylonitrile homopolymer wereadded to 100 milliliters of N,N-dimethyl acetamide containingapproximately 1.0 gram of titanium dioxide. The mixture was stirred andheated for 240 minutes at 100 C. It was then quickly cooled to roomtemperature and the color measured. This sample was used as a control.The purity of the control sample is set forth below. Subsequently, likesamples were prepared but with 2.5 grams of an inhibiting agentcontaining 0.5 gram of paraformaldehyde and 2.0 grams of one of thefollowing: triethyl phosphite, tributyl phosphite, tris (2-ethylhexyl)phosphite, trihexyl phosphite and triisoctyl phosphite. The purity isset forth below.

Table III Inhibitor Percentage Used The tests for color indicative ofapproaching whiteness used throughout the examples consist ofmeasurements of purity as calculated from the tristimulus valuesdetermined on a General Electric spectrophotometer by the methodsrecommended by the Standard Observer and Coordinate System of theInternational Commission on Illumination, as fully set forth in theHandbook of Colorimetry published by The Technology Press, MassachusettsInstitute of Technology in 1936.

The compositions of the instant invention present many advantages. Forexample, products formed from the polymer solutions of the instantinvention are free of objectionable color and therefore of greatercommercial value. In preparing the polymer solutions, heat may beapplied without the danger of color formation and the solutions, ifnecessary, may stand for prolonged periods and remain free of color. Theinhibiting agents are readily available and inexpensive. Therefore, nogreat increase in production cost is necessary. The compositionscontaining the inhibitors may be prepared without going through detailedand elaborate procedures that necessitate expensive changes in thedesign of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparentlywidely different embodiments of this invention can be made withoutdeparting from the spirit and scope thereof. Accordingly, it is to beunderstood that this invention is not to be limited to the specificembodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer containing at least80 percent of polymerized acrylonitrile and up to 20 percent of anotherpolymerizable monoolefinic monomer copolymerizable therewith, a solventtherefor, and an inhibiting agent containing about 20 percent ofparaformaldehyde and about 80 percent, based on the total weight of saidinhibiting agent, of an organic phosphite selectedfrom the groupconsisting" of triethyl phosphiteftributyl phosphite,tris(2-ethylhe'xyl) phosphite, trihexyl phosphite and triisoctyl phosphite.

21A new composition of matter as defined in claim 1 wherein the polymeris a copolymer containing from to 98 percent of acrylonitrile and from 2to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith. 3. A new compositionof matter as defined inclaim 1 wherein the polymer is a blend of 80 to 99 percent of (A) acopolymer containing to 98 percent of acrylonitrile and 2 to 10 percentof vinyl acetateand 1 to 20 percent of (B) a copolymer containing 10. to70 percent of acrylonitrile and 30 to 90 percent of2-methy'l-5-vinylpyridine.

4. A new composition of matter as defined in claim 1 wherein the polymeris polyacrylonitrile. I v

5. A new composition of a matter as defined in claim 1 wherein theorganic phosphite is triethyl phosphite. I

6. A new composition of matter as defined in claiml wherein the organicphosphite is tributyl phosphite.

7. A new composition of matter as defined in claim 1 wherein the organicphosphite is tris (Z-ethylhexyl) phosphite.

8. A new composition of matter as defined in claim 1 wherein the organicphosphite is trihexyl phosphite.

9. A new composition of matter as defined in claim 1 wherein the organicphosphite is triisoctyl phosphite.

10. A new composition of matter as defined in claim 1 wherein thesolvent is N,N-dimethylacetamide.

11. A new composition of matter comprising a polymer blending of (A) acopolymer containing 90 to 98 percent of acrylonitrile and 2 to 10percent of another polymerizable mono-olefinic monomer and (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of a vinyl-substituted tertiary heterocyclic amine, said blendhaving an overall vinyl-substituted tertiary heterocyclic amine contentof from 2 to 10 percent, based on the weight of the blend, a solventtherefor, and an inhibiting agent containing about 20 percent ofparaformaldehyde and about 80 percent, based on the total weight of saidinhibiting agent, of an organic phosphite selected from the groupconsisting of triethyl phosphite, tributyl phosphite, tris(Z-ethylhexyl) phosphite, trihexyl phosphite and triisoctyl phosphite.

12. A new composition of matter comprising a copolymer containing 80 to98 percent of acrylonitrile and 2 to 20 percent of vinyl acetate, asolvent therefor, and 0.1 to 20 percent, based on the total weight ofthe polymer, of an inhibiting agent, said inhibiting agent containingabout 20 percent of paraformaldehyde and about 80 percent, based on thetotal weight of said inhibiting agent, of an organic phosphite selectedfrom the group consisting of triethyl phosphite, tributyl phosphite,tris (2-ethylhexyl) phosphite, trihexyl phosphite and triisoctylphosphite.

13. A new composition of matter comprising a polymer blend of 80 to 99percent of (A) a copolymer containing 90 to 98 percent of acrylonitrileand 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of 2-methyl-5-vinylpyridine, a solvent therefor, and 0.1 to 20percent based on the total weight of the polymer, of an inhibiting agentcontaining about 20 percent of paraformaldehyde and about 80 percent,based on the total weight of said inhibiting agent, of an organicphosphite selected from the group consisting of triethyl phosphite,tributyl phosphite, tris (2-ethylhexyl) phosphite, trihexyl phosphite,and triisoctyl phosphite.

14. A new composition of matter comprising a polymer containing at least80 percent of polymerized acrylonitrile and up to 20 percent of anotherpolymerizable mono-olefinic monomer copolymerizable therewith, a solventtherefor, and 0.1 to 20 percent based on the total weight of thepolymer, of an'inhibiting agent, said inhibit- '4' ing agent containingabout 20 percent of paraformaldehyde and about 80 percent, based on thetotal weight of said inhibiting agent, of an organic phosphite selectedfrom the groupvconsisting of triethyl phosphite, tributyl phosphite,tris (2-ethylhexyl) phosphite, trihexyl phos phite and triisoctylphosphite.

15. A method for preparing a new composition of matter comprising mixinga polymer containing at least 80 percent of polymerized acrylonitrileand up to 20 percentof another polymerizable mono-olefinic monomercopolymerizable therewith, a solvent therefor, and an inhibiting agentcontaining about 20 percent of paraformaldehyde and about 80 percent,based on the total weight of said inhibiting agent, of an organicphosphite selected from the group consisting of triethyl phosphite,tributyl phosphite, tris (Z-ethylhexyl) phosphite, trihexyl phosphiteand triisoctyl, and heating the mixture to form a homogeneous solution.

16. The method as defined in claim 15 wherein the organic phosphite istributyl phosphite.

rS-vinylpyridine, a solvent therefor, and 0.1 to 20 percent, based onthe total weight of the polymer, of an inhibiting agent, said inhibitingagent containing about 20 percent of paraformaldehyde and about 80percent, based on the total weight of said inhibiting agent, oftriisoctyl phosphite, and heating the mixture to a temperature in arange 0t 25 C. to the boiling point of said mixture to form ahomogeneous solution.

References Cited .in the file of this patent UNITED STATES PATENTSScheiderbauer -..'Mar. 28, 1950 Stanin'et a1 June 16,1953

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST80 PERCENT OF POLYMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHERPOLYMERIZABLE MONOOLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENTTHEREFOR, AND AN INHIBITING AGENT CONTAINING ABOUT 20 PERCENT OFPARAFORMALDEHYDE AND ABOUT 80 PERCENT, BASED ON THE TOTAL WEIGHT OF SAIDINHIBITING AGENT, OF AN ORGANIC PHOSPHITE SELECTED FROM THE GROUPCONSISTING OF TRIETHYL PHOSPHITE, TRIBUTYL PHOSPHITE, TRIS(2-ETHYLHEXYL) PHOSPHITE, TRIHEXYL PHOSPHITE AND TRIISOCTYL PHOSPHITE.